備忘: Railsで古い日付を JST の TimeWithZoneに変換すると時刻がずれる

追記

コメントで教えていただきました！

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以下、元記事

ふかぼりきれておらず事象だけのメモ

環境

ruby: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin22]
rails: 7.1.2

現象

❯ TZ=UTC rails c
Loading development environment (Rails 7.1.2)
irb(main):001> Rails.application.config.time_zone
=> "UTC"
irb(main):002> Time.now.zone
=> "UTC"
irb(main):003> Time.zone.parse("1800/01/01 00:00:00").iso8601
=> "1800-01-01T00:00:00Z"
irb(main):004> Time.zone.parse("1800/01/01 00:00:00").utc.iso8601
=> "1800-01-01T00:00:00Z"
irb(main):005> Time.zone.parse("1800/01/01 00:00:00").in_time_zone("UTC").iso8601
=> "1800-01-01T00:00:00Z"
irb(main):006> Time.zone.parse("1800/01/01 00:00:00").in_time_zone("Tokyo").iso8601
=> "1800-01-01T09:18:59+09:18"
irb(main):007> Time.parse("1800/01/01 00:00:00").iso8601
=> "1800-01-01T00:00:00+00:00"
irb(main):008> Time.parse("1800/01/01 00:00:00").utc.iso8601
=> "1800-01-01T00:00:00Z"
irb(main):009> Time.parse("1800/01/01 00:00:00").in_time_zone("UTC").iso8601
=> "1800-01-01T00:00:00Z"
irb(main):010> Time.parse("1800/01/01 00:00:00").in_time_zone("Tokyo").iso8601
=> "1800-01-01T09:18:59+09:18"

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❯ rails c
Loading development environment (Rails 7.1.2)
irb(main):001> Rails.application.config.time_zone
=> "Tokyo"
irb(main):002> Time.now.zone
=> "JST"
irb(main):003> Time.zone.parse("1800/01/01 00:00:00").iso8601
=> "1800-01-01T00:00:00+09:18"
irb(main):004> Time.zone.parse("1800/01/01 00:00:00").utc.iso8601
=> "1799-12-31T14:41:01Z"
irb(main):005> Time.zone.parse("1800/01/01 00:00:00").in_time_zone("UTC").iso8601
=> "1799-12-31T14:41:01Z"
irb(main):006> Time.zone.parse("1800/01/01 00:00:00").in_time_zone("Tokyo").iso8601
=> "1800-01-01T00:00:00+09:18"
irb(main):007> Time.parse("1800/01/01 00:00:00").iso8601
=> "1800-01-01T00:00:00+09:00"
irb(main):008> Time.parse("1800/01/01 00:00:00").utc.iso8601
=> "1799-12-31T15:00:00Z"
irb(main):009> Time.parse("1800/01/01 00:00:00").in_time_zone("UTC").iso8601
=> "1799-12-31T15:00:00Z"
irb(main):010> Time.parse("1800/01/01 00:00:00").in_time_zone("Tokyo").iso8601
=> "1800-01-01T00:18:59+09:18"